Glass fibers and glass fiber strands have been used before in the art to produce various types of glass fiber mats for use as reinforcement material. The basic principles of mat-making are well known in the art and fully described in the book entitled The Manufacturing Technology of Continuous Glass Fibers by K. L. Lowenstein, published by the Elsevier Publishing Company, 1973, at pages 234 to 251.
A particular utility for glass fiber mats is in the reinforcement of resinous or polymeric materials since the presence of an integrally molded glass fiber mat substantially increases the strength of these materials. Usually, the mat and a molten resin are processed together to form a thermoset or thermoplastic laminate. Thermoplastic laminates are particularly attractive for use in the aircraft, marine, and automotive industries since they may be reheated into a semi-molten state and then stamped into panels of various shapes such as doors, fenders, bumpers, and the like. Similarly, thermosetting mats may be used in pultrusion processes for the reinforcement of ladder rails, electrical components, and window lineals.
It is important in all of these applications that the glass mats used to make these laminates have as uniform a fiber density distribution as possible. If a non-uniform density mat is used for reinforcement purposes, the products produced therefrom may have a substantial variation in their strength since some areas will be weaker due to the lack of glass fiber reinforcement while others will be stronger. Even more important is the need to insure that the glass fiber mat flows and moves freely within the laminate during stamping operations in order to impart uniform strength to the final components which are produced.
In the production of continuous strand mats, a plurality of strand feeders are positioned above a moving belt or conveyor, typically a continuously driven, flexible, stainless steel chain or other perforated surface. The strand feeders are reciprocated or traversed back and forth above the conveyor parallel to one another and in a direction generally perpendicular to the direction of motion of the moving conveyor. Strands composed of multiple glass fiber filaments are fed to the feeders from a suitable supply source such as a plurality of previously made forming packages.
It is also well known in the art that the feeder can act as an attenuator to attenuate glass fibers directly from a glass fiber-forming bushing and eventually deposit strand formed therefrom directly onto the conveyor as described by Lowenstein, supra, at pages 248 to 251 and further illustrated in U.S. Pat. Nos. 3,883,333 (Ackley) and 4,158,557 (Drummond) and U.S. Pat. Nos. 4,963,176 (Bailey, et al.) and 4,964,891 (Schaefer).
Each feeder apparatus provides the pulling force necessary to advance the strand from the supply source and eventually deposit it upon the surface of the moving conveyor. In a typical production environment, as many as 12 to 16 such strand feeders have been used simultaneously with one another to produce a glass fiber mat. Notable prior art references describing the operation and control of such reciprocating feeders can be found in U.S. Pat. Nos. 3,915,681 (Ackley) and 4,340,406 (Neubauer, et al.) as well as U.S. Pat. No. 4,963,176 (Bailey, et al.) and U.S. Pat. No. 4,964,891 (Schaefer), all of which have been assigned to the same assignee as the subject matter of the present invention.
Once the strand has been deposited on the conveyor to form a random pattern of loose glass strand, mechanical integrity must somehow be imparted to it so that these loose strands can be subsequently handled as a mat and eventually fabricated into a finished laminate. To accomplish this, one method known in the art is to pass the loose strands through a needling loom wherein a plurality of barbed needles are reciprocated up and down so as to penetrate the strands and thereby entangle them with one another. This technique is further described in U.S. Pat. Nos. 3,713,962 (Ackley); 4,277,531 (Picone); and 4,404,717 (Neubauer, et al.). Another method by which the loose strand can be bound into the form of a mat is to impregnate the strand with a chemical resin and then melting it so that the individual strands comprising the mat structure become bonded to one another. Usually, this melting operation takes place inside an oven through which both the conveyor and the strand continually pass. The oven must be of a sufficient length and heated to such a degree that the residence time of the glass strand and resin inside the oven is long enough to thoroughly melt the resin and dry any excess moisture from the strand. Ovens having a length of 20 feet (6.1 meters) or more are not uncommon. As was pointed out in Lowenstein, supra, at pages 245 to 246, the oven is often the largest section of a chopped-strand mat line and the same can be said for continuous strand mat lines as well. Besides the physical size of the oven, there is also the expense associated with its construction and keeping it in continuous operation.
Thus, there exists a need, especially in industrial production environments, to eliminate the use of an oven for melting and/or curing resin impregnated continuous strand fiber glass mats.
There also exists a need to fabricate continuous fiber glass strand mats having uniform density and mechanical properties.
There also exists the need to insure that the resin incorporated to bond the individual glass fiber strands together with one another is distributed as uniformly as possible so that the above-mentioned uniform physical properties will result in both the finished mat and the subsequent laminate sheets and products produced therefrom.
As now will become apparent from the remainder of this disclosure, the instant invention adequately meets these needs by providing an improvement over the present state of the art.